UNDERSTANDING VARIATION IN PARTITION COEFFICIENT, Kd ...

J.3.0 Approach in Developing K d Look-Up Table
The uranium K d values listed in Table J.5 are plotted in Figure J.4 as a function of pH. The K d
values exhibit large scatter. This scatter increases from approximately 3 orders of magnitude at
pH values below pH 5, to approximately 3 to 4 orders of magnitude from pH 5 to 7, and
approximately 4 to 5 orders of magnitude at pH values from pH 7 to 9. This comparison can be
somewhat misleading. At the lowest and highest pH regions, it should be noted that 1 to 2 orders
of the observed variability actually represent uranium K d values that are less than 10 ml/g. At pH
values less than 3.5 and greater than 8, this variability includes extremely small K d values of less
than 1 ml/g.
Log Kd (ml/g)
7
6
5
4
3
2
1
0
-1
-2
2 3 4 5 6 7 8 9 10 11
Figure J.4. Uranium K d values used for development of K d look-up table.
[Filled circles represent K d values listed in Table J.5. Open
symbols (joined by dotted line) represent K d maximum and
minimum values estimated from uranium adsorption
measurements plotted by Waite et al. (1992) for ferrihydrite
(open squares), kaolinite (open circles), and quartz (open
triangles). The limits for the estimated maximum and
minimum K d values based on the values in Table J.5 and
those estimated from Waite et al. (1992) are given by the “x”
symbols joined by a solid line.]
J.19
pH